I've spent about four hours over the past two mornings picking sandstone rocks out of one of our fields. For years we only planted corn or sorghum there, and the rocks weren't an issue since the harvester cut the stalks several inches off the ground. Now that we're planting cool-season forages in this field, we either have to get rid of the rocks or be prepared to constantly bend/break/dull the blades on our cutter-condition (which cuts only 1-2" from the ground).
We did a good job of removing most of the rocks from the real trouble spots about three years ago and have had minimal trouble ever since then. The main reason for that, though, was that we have been no-till planing the rye/oats and minimal-till planting the corn/sorghum since then. We needed to break the ground before planting this time, though, and the disking process unearthed lots of buried rocks.
Even though there are rocks throughout the 40 acre field, we can get the worst places cleaned out after another hour or two of picking. By then we out to have enough rocks to fill in a hole, serve as the foundational base for a small "heavy use" area, or build a decorative driveway entrance leading to our milking barn.
Just kidding about that last one.